Thank you for posting your experience with the head unit and Maestro. I am thinking of doing something very similar to my 2016 4Runner (SR5 Premium). I was wondering if I could ask a few questions before I jump into this modification.
After you installed everything, what functions were you able to program the steering wheel buttons to do?
Anything you want reallym depending on the radio's capabilities. For instance, it has a press and hold feature. I programmed it to mute if I hold volume down. My steerin wheel has a back button, but the radio doesn't need it so I set that to play/pause. If I hold the up arrow down, it rings up the custom gauges.
What do the up/down/left/right, back, and mode/mute buttons on the left side of the steering wheel do?
What do the push to talk, phone off hook, phone on hook buttons on the right side of the steering wheel do?
Each button is custom programmable for press and release and another function press and hold. Go toe the Maestro Website and there is a link there for "Test drive Maestro", then select RR as the product. It will walk you through a simulation on programming it.
iDatalink - Maestro - Home
What about the disp button? Does it still cycle through the options on the display between the speedometer and tachometer?
I understand the factory backup camera functions just like it did with the stock head unit. Is that the case?
yup
What about the factory navigation GPS? If I installed a head unit with navigation (e.g., Pioneer AVIC 8200NEX), would it use the factory GPS?
I placed my Kenwood GPS antenna in the same place as the OEM one, you'll see it mounted behind the OEM radio on a metal bracket underneath the dash. CarPlay for now only uses Apple maps. The Kenwood DNX-573s has built in Garmin navigation or uses Apple maps in Carplay, but that radio can be $200 - $300 more than a DDX-9703s.
I installed a Kenwood DDX9902s in my old 2008 4Runner in conjunction with an Axxess ASWC-1 steering wheel button interface and was able to get the volume up/down buttons, up/down buttons (mapped to jump to next track/previous track), and mode button (mapped to long press to activate Siri) with good results. I also installed a backup camera by running wires through the headliner (a pain I hope never to deal with again). I loved CarPlay and have really found the stock head unit in my 2016 with Entune Premium to be severely lacking in functionality.
CarPlay rocks, no doubt. Even better now that you can finally re-arrange the icons with iOS 10. My talk button brings up Siri no problem.
Thank you for your time and expertise.